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GEOL. 363 : Mineral Deposits 3(3/3-0/0) MWF 0800-0900 GB 200 /110 “ Formation, characteristics and distribution of metallic and non-metallic mineral deposits ” Introduction Genesis of Mineral Deposits Geology of Mineral Deposits Excursion : Sat. 11 Aug. 2001 5 hrs. 10 ,, 30 ,, Introduction • Definition of mineral deposits and related terms • Morphology of mineral deposits • Modes of mineral deposition. • Plate tectonics and mineralization • Classifications of mineral deposits What is a mineral deposit ? A mineral deposit is a place where valuable mass of economic mineral (or minerals) is formed in varying size, shape and orientation. The ore body or valuable mass of economic minerals is normally outlined by cut-off grade. Morphology of an ore body can be: tabular, cylindrical, pipe, massive, lenses, nest, massive etc. How is a mineral’s concentration factor determined? Concentration factor, the increase in concentration of a mineral required to form an ore. What is the difference between ore and gangue? • Ore is rock that contains economic concentrations of metallic minerals. • Gangue is non-economic minerals associated with ores. Pyrrhotite-rich, magmatic sulfide blebs partly altered to chalcopyrite. Little Stobie Mine, Sudbury Massive pyrrhotite (Po; tan and yellow) and pentlandite (Pn; white) Sudbury massive ores in reflected light under crossed polars. Pentlandite grains are intergrown with pyrrhotite and constitute the main nickel mineral for which t h e s e o r e s a r e m i n e d. Some of the ores from the Sudbury nickel district contain significant amounts of cubanite (CuFe2S3). Cubanite forms a complete solid solution series with chalcopyrite, and the single solid formed at high temperatures may exsolve with d e c l i n i n g t e m p e r a t u r e s. What is the difference between a reserve and a resource? • Reserves are resources that can be economically extracted using existing technology •The volume of reserves is much less than the volume of resources Morphology of Mineral deposits An orebody is a mixture of valuable minerals and waste rock. Each orebody, which has a definite size and shape, is a mass that contains enough valuable mineral to be mined and p r o c e s s e d a t a p r o f i t. S h a p e s o f o r e b o d i e s c a n b e c l a s s i f i e d a s: 1. D i c s c o r d a n t 2. C o n c o r d a n t i.e. vein type deposits i.e. stratiform ore deposits A: Discordant Orebodies Regularly shaped bodies Tabular orebodies Tubular orebodies Irregularly shaped bodies Disseminated deposits Irregular replacement deposits B: Concordant Orebodies Sedimentary host rocks Igneous host rocks Volcanic hosts Plutonic hosts Metamorphic host rocks Residual deposits Supergene enrichment Skarn A replacement of limestone (calcium carbonate) or other carbonate-rich rocks adjacent to an intrusive contact by calc-silicate minerals usually through the addition of Si and o t h e r e l e m e n t s. Massive Sulfide Orebody Anticlinal fold in sandstones and shales, United Kingdom. The white material in the hinge of the fold at the center of the photograph is quartz, and fills a void that opened up during folding. Such filled-in features are called saddle reefs. How can minerals deposits be formed? Magmatic mineral deposits concentrated in igneous rocks; Residual mineral deposits formed by weathering reactions at the earth’s surface. Placer deposits are sorted and distributed by flow of transporting media such as water, wind and ice; Sedimentary mineral deposits are precipitated from a solution, typically sea water; Metamorhogenic mineral deposits form in association with metamorphism Hydrothermal mineral deposits form in association with magma and water; Distribution of major tectonic plates Classifications of Mineral Deposits